Understanding The Requirements For Effective Nasal Drug Delivery - Pharmaceutical Technology

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PharmTech Europe

Understanding The Requirements For Effective Nasal Drug Delivery

Pharmaceutical Technology Europe
Volume 22, Issue 9

Controlling droplet size

Figure 1: Schematic of a nasal spray device.
Developers of nasal spray products tune an array of variables, some relating to the formulation others to the device, to achieve a target droplet size profile. Nasal spray devices usually incorporate a manually driven spray pump, which when actuated by the patient, pushes the liquid formulation through an orifice, thereby applying energy for atomisation (Figure 1). Aspects of spray pump design, such as the precompression ratio, and the geometry, length and orifice size of the actuator determine the shear force applied during use, which, in turn, influences the size of the droplets produced. The number and size of doses for which the product is intended will also be taken into account when determining the design of the device.

In terms of the formulation, modifying properties by changing the composition alters the response to conditions imposed by the device. A product may be solution- or suspension-based, with excipients levels controlled to meet atomisation and stability requirements. Viscosity modifiers such as glycerin, polyvinylpyrrolidone (PVP) and various cellulose-derivatives are especially common because the viscosity of the formulation has a marked impact on behaviour, with more viscous liquids requiring greater energy for dispersion to the same droplet size. Surface tension is also an important physical property and may affect droplet size.

Developing an optimal product relies on the effective manipulation of these influential variables, but this is only possible with reference to relevant droplet size data. Laser diffraction meets this need by providing real-time particle size analysis through a spray event.

Using laser diffraction for nasal spray analysis

With laser diffraction, the size of droplets in a spray is determined from the scattering pattern produced as particles pass through a collimated beam of light. Smaller particles scatter light weakly at wider angles, while larger particles produce a stronger signal at narrower angles. The technique is non-destructive, requires no calibration and is suitable for even concentrated sprays, providing that appropriate mathematical algorithms are used to analyse the scattered light pattern.

To be effective for spray measurement, laser diffraction systems must meet some essential criteria, including the ability to rapidly acquire data to track the droplet size of a spray as it evolves during a single actuation of the device. For nasal sprays, a wide dynamic range is needed so that the very large droplets (up to 600 m in size) delivered at the beginning and end of a spray pump actuation can be detected, along with any fines. This enables researchers to understand each phase of atomisation during actuation, aiding the process of product optimisation.


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